1. Field of the Invention
The present invention relates to an apparatus for concealing error data of pixel data in a received digital image signal which is applied to recording and/or reproducing a digital image signal with a digital VTR which uses, for example, a highly efficient coding technique.
2. Description of the Prior Art
When a digital video signal is recorded on a recording medium such as a magnetic tape, the amount of information of the digital video signal is large. In recent years, to deal with the digital video signal, highly efficient coding techniques which compress such a digital video signal have been generally employed. An example of the highly efficient coding techniques, ADRC (Adaptive Dynamic Range Coding) technique is known.
The ADRC technique is an highly efficient coding technique which obtains a dynamic range defined by a maximum value and a minimum value of a plurality of pixels contained in a two-dimensional block of a signal and then encodes the signal corresponding to the dynamic range, as disclosed in U.S. Pat. No. 4,703,352.
The encoded output of an ADRC process is constructed of data called important word and quantized data of each pixel. The important word consists of a dynamic range DR and a minimum value MIN. If an error occurred in the important word, the error would propagate to all pixels of the block. Thus, this data is called the important word. With respect to errors of quantized data, since the ADRC process does not compress image data in space direction, even if an error occurs in quantized data upon transmitting, the error does not propagate to decoded data of other pixels. Thus, if a pixel with an error were interpolated with pixel data adjacent thereto, the error would become unremarkable. Such an interpolating process is referred to as a concealing process.
In the conventional pixel-by-pixel concealing technique, a pixel with an error is substituted with the average value of the adjacent pixels or a pixel value adjacent thereto. Thus, the resolution is deteriorated at the pixel with the error.
Even if visual deterioration is none or small, when multiple-dubbing where dubbing is repeated is performed, the image quality of the restored image may be deteriorated since a decoded value is largely apart from a real decoded value.